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    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        //typeof 查看元素属性

        console.log(123);
        console.log(typeof 123);

        console.log('123');
        console.log(typeof '123');

        console.log(true);
        console.log(typeof true);

        //var obj = null 
        // var obj = {name:'123',age:'121'}
        //obj = null obj用完之后设置
        console.log(null);
        console.log(typeof null);

        console.log(10 * 'a');//NaN
        console.log(10 * 'a' === NaN);//false
        //判断表达式是否为NaN
        console.log(isNaN(10 * 'a'));//true

        console.log(null === null);
        console.log(undefined === undefined);
        console.log([] === []);
        console.log({} === {});









    </script>
</body>
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